A. W von Hofmann was the first to isolate sorbic acid (2,4-hexadienoic acid) in 1859 (by distilling oil pressed from the berries of mountain ash trees.). The distillation yields the corresponding lactone, which Hofmann then converted to the acid by hydrolysis. Its antimicrobial properties were not extensively explored until after the close of World War II. Since the 1950's, sorbic acid (E200) has been used extensively worldwide as a preservative in a vast array of foods. For example, sorbic acid has been used since the late 1950's as a preservative in white wines. Sorbic acid and its salts (notably potassium sorbate, E202) are also used as inhibitors of Clostridium botulinum in processed meat products. Sorbic acid and its salts are commodity products; worldwide production of sorbates in 2008 was approximately 65,000 metric tons (i.e., tonnes; 71,650 US short tons).
The benefits of sorbates as food preservatives are two-fold: sorbates inhibit a very wide spectrum of bacteria, yeasts, and molds; and sorbates have extremely low toxicity (lower even than table salt, NaCl). Sorbates are “generally regarded as safe” (GRAS) by the U.S. Food and Drug Administration.
There are several known protocols for producing sorbic acid and sorbates. Commercial quantities are typically produced by polymerizing crotonaldehyde and ketene to form an intermediate polyester, decomposing the polyester to yield a crude sorbic acid, and then subjecting the crude sorbic acid to a variety of purification steps to yield various grades of sorbic acid (e.g., food grade). The intermediate polyester is decomposed by a number of means, including treating it with strong acid, strong base, or via heat. The required decomposition step is problematic because it yields unwanted, colored by-products. To yield the highest grades of product (i.e., food grade sorbate or better) multiple purification steps are required.
Japanese Examined Patent Application Publication No. 44-26646 discloses a process for producing sorbic acid in which the polyester obtained by the reaction between crotonaldehyde and ketene is decomposed with hydrochloric acid, followed by cooling and filtrating the resulting reaction mixture to yield crude sorbic acid. The crude sorbic acid is then dissolved in hot water to which is added activated carbon. The reaction mixture is filtered hot, and the filtrate is gradually cooled to yield crystalline sorbic acid.
A related protocol is described in Japanese Unexamined Patent Application Publication No. 54-163516. Here, the polyester obtained from reacting crotonaldehyde and ketene is decomposed with hydrochloric acid in the presence of a urea compound. The resulting decomposition reaction mixture is filtered to yield crude sorbic acid. Aqueous sodium hydroxide solution is added to the crude sorbic acid to yield an aqueous sodium sorbate solution. The aqueous sodium sorbate solution is treated with activated carbon, neutralized, and cooled to crystallize the purified sorbic acid.
See also U.S. Pat. No. 6,525,218, which describes a process in which the intermediate polyester (the reaction product between crotonaldehyde and ketene) is hydrolyzed with an aqueous hydrochloric acid solution having a concentration of from 3 to 10% by weight under a pressure greater than atmospheric pressure.
These prior art processes for making sorbates are less than ideal because of the formation of by-products (tar, etc. formed during the decomposition step), and yield losses during the solid-liquid separation steps.
1,3-Pentadiene (also known as piperylene) is a volatile, flammable, linear five-carbon hydrocarbon. It is widely used as a monomer in the production of plastics, adhesives, and resins. It is produced commercially as a by-product of ethylene production via the catalytic cracking of naphtha. There is no other means known to produce 1,3-pentadiene in commercial quantities. However, there have been efforts to genetically engineer microorganisms such as yeast to produce 1,3-pentadiene. See Casasa et al. (1 Jul. 2004) “Pentadiene production from potassium sorbate by osmotolerant yeasts,” International Journal of Food Microbiology, 94(1):93-96.